1. Field of Invention
The present invention relates to a magnetic head for floppy disc drive.
2. Background of Related Art
In general, since a FDD (floppy disc drive) is installed within a personal computer, the magnetic head of the FDD is likely to generate a reading error due to an electromagnetic noise from a CTR, a switching source and such. Then, in order to avoid such a reading error, it is a general countermeasure to shield the magnetic head with a magnetic material having a high permeability such as permalloy or ferrite (hereinafter referred this general magnetic head to as "conventional example 1").
Now, recently in a note-type of personal computer (note personal computer) and such low-profile FDD having half-inch thickness is used. In this type, it has been difficult to shield the magnetic head with the material having a high permeability such as permalloy or ferrite. As a countermeasure to that, there is what is disclosed in the patent laid-open No. Hei 7-235013 (hereinafter referred to as "conventional example 2").
The magnetic head 1 of the conventional example 2 comprises roughly, as shown in FIG. 5, a front chip core 2 having a read/write gap G.sub.1 and an erasing gap G.sub.2, a first slider 4a and a second slider 4b which are made of a non-magnetic material (not shown) and form the front core 3 while being formed in unit with the front chip core 2 across the front chip core 2, each side of which slides (upper in FIG. 5) on a magnet recording medium (not shown), a back yoke 5 which is made of a magnetic material having a high permeability such as permalloy or ferrite and contacts to the other side of the front core 3 and a read/write core 6 and an erasing coil 7 later mentioned respectively.
The back yoke 5 comprises a hollow square pillar-like outer body 8 whose tip end contacts to the afore-mentioned front core 3, a block body 40 comprising a bottom portion 9 formed at the proximal side of the outer body 8 and similarly shaped three leg portions 10a, 10b and 10c (hereinafter referred to as "the first, second and third leg portion" viewing from right to left direction in FIG. 5) which stand upright on the bottom portion 9 in juxtaposing manner, each tip ends of which contacts to the afore-mentioned front chip core 2 to form a closed magnetic circuit (not shown) together with the front chip core 2 and afore-mentioned bottom portion 9.
The outer body 8 is of approximately a hollow square pillar shape formed by connecting two opposing short side portions (hereinafter referred to as "first short side portion 8.sub.11 " positioned right below in FIG. 5 and "second short side portion 8.sub.12 " positioned left upper in FIG. 5) and two opposing long side portions (hereinafter referred to as "first long side portion 8.sub.21 " right upper in FIG. 5 and "second long side portion 8.sub.22 " left below in FIG. 5), and between the first short side portion 8.sub.11 and the first leg portion 10a and between the second short side portion 8.sub.12 and the third leg portion 10c, a window 11 for a lead wire is formed. From the window 11 for lead wire, a lead 6a of the read/write coil 6 and a lead 7a of the erasing coil 7 are drawn out and connected to outer connecting terminals of a not shown FPC (flexible printed circuit board) etc.
The first and third leg portions 10a and 10c are inserted in the afore-mentioned read/write coil 6 and the erasing coil 7.
In the magnetic head 1 of this conventional example 2, the back yoke 5 is made of magnetic material having a high permeability such as Mn--Zn ferrite, the outer body 8 and the bottom portion 9 function as a magnetic shield. And, in this case, since the back yoke 5 provided on the magnetic head 1 functions as a magnetic shield, a problem of the difficulty of the magnetic shielding generated in the case where the magnetic shield is carried out in a low profile FDD in the conventional example 1 is planned to be improved.
Now, in the conventional example 2, although that is the type in which the coils are of lead wire, it is thinkable, in place of the coil to be used in the conventional example 2, to use a bobbin type of coil with terminals (hereinafter referred to as "bobbin coil with terminals") which is formed in such a manner as, as a coil, a bobbin made of a high heat resistance resin such as LPC and metal terminals are molded in a unit and with such bobbin wirings are coupled. In this case, in order to accommodate a terminal stand for the bobbin coil with terminals, the outer body is necessary to make large, for that reason, it has been difficult to miniaturize the magnetic head.
Further, in the back yoke 5 of the conventional example 2, as well as in manufacturing a ceramic, it is formed by molding a powder of Mn--Zn ferrite and such and a binder to a given shape with a mold, then is adapted to be sintered at a high temperature while burning out the binder and solidifying the powder simultaneously. Accordingly, if the leg portions (10a, 10b and 10c) are made slimmer, there is anxiety that the leg portions are suffered from being bent or generating any crack. For that reason, in the conventional example 2, it has been difficult to make the leg portions slimmer which is led to miniaturize the apparatus as a whole.
Against such problem as bending or generating of crack on the leg portions is generated after sintering, there is one magnetic head in which the leg portions are made slimmer by a post-machining after sintering. Such an example is illustrated in Japanese patent laid-open publication No. Hei 10-40525 (hereinafter referred to as "conventional example 3).
The magnetic head 1 of the conventional example 3 comprises, as shown in FIGS. 6 and 7, a front core 3 which consists of a slider 4 and a front chip core 2 to be inserted in a hole 12 formed in the slider 4 and a back yoke 5 made of magnetic material having high permeability which is manufactured showing as follows.
The back yoke 5 is different, compared with the one of the conventional example 2, in that it has no window 11 for the lead on the bottom portion 9, that on the second long side portion 8.sub.22 the first, second and third projections 13a, 13b and 13c which extend to the first, second and third leg portions 10a, 10b and 10c respectively are formed and that the first and second short side portions 8.sub.11 and 8.sub.12 are provided with cut outs 14 respectively.
And, in this back yoke 5 is, at the time of being powder-molding and sintered, as shown in a dotted line 15 in FIG. 6, the first, second and third leg portions 10a, 10b and 10c are connected to the outer body 8 (the first, second and third projections 13a, 13b and 13c), and by a post-machining such as cutting for grooving, the portions circled with the dotted line 15 in FIG. 6 are removed to separate the first, second and third leg portions 10a, 10b and 10c into a given width (thickness). Due to this cutting for grooving, the cut out 14 is formed on the first and second short side portions 8.sub.11 and 8.sub.12. Through the cut out 14, the lead 6a of the read/write coil 6 and the lead 7a of the erasing coil 7 are drawn out.
In the magnetic head 1 of the conventional example 3, the first, second and third leg portions 10a, 10b and 10c are, at the time of molding and sintering, connected to the outer body 8 and which prevent the leg portions 10a, 10b and 10c from being bent and being suffered from generating cracks.
However, in the above mentioned magnetic head 1 of the conventional example 3, when machining the first, second and third leg portions 10a, 10b and 10c into the given thickness, simultaneously on the outer body 8 the cut out 14 is formed, which happens to cause to bring about easily entering of outer noises through this cut out 14.
Further, since the magnetic head 1 of the conventional example 3 is not provided with the bobbin coil with terminal stand, when connecting terminal of coil to the external connecting terminal such as FPC (flexible printed circuit board), it is necessary to such work having the lead of coil in hand with tweezers. Therefore, much steps for such work are necessary and there has been a case where lead of coil and external connecting terminal are damaged with tweezers to break them.
Now, as an example of the magnetic head which uses the afore-mentioned bobbin coil with terminals, there is what is shown in FIG. 8 (hereinafter referred to as "conventional example 4").
This magnetic head 1 comprises, in general, as shown in FIG. 8, a front chip core 2 having a read/write gap G.sub.1 (operation gap) and an erasing gap G.sub.2 (operation gap), a non-magnetic material made slider 4 forming the front core 3 formed with a sliding surface S on one side thereof due to the front chip core 2 inserted in, a back yoke 5 made of a magnetic material having a high permeability such as Mn--Zn ferrite to be connected to the other side of the front core 3, a read/write coil 6 and an erasing coil 7.
The back yoke 5 comprises a block body 40 which is formed in the shape of approximately a hollow square pillar-like outer body 8 and the bottom portion 9 formed on the proximal side of the outer body 8 and the first, second and third leg portions 10a, 10b and 10c which stand upright on the second long side portion 8.sub.22 in the bottom portion 9 in juxtaposing manner. The portions of the first and second short side portions 8.sub.11 and 8.sub.12 which are located near the second long side portion 8.sub.22 are formed with the cut outs
The read/write coil 6 and the erasing coil 7 are of the type which is the bobbin with the terminals obtained by being molded in a unit, in which a bobbin 20 made of a high temperature resistance resin such as LCP holds the wirings of the read/write coil 6 and the erasing coil 7.
The bobbin 20 is constituted, in general, from an approximately cylindrical bobbin body 20a with which a wiring 6A of the read/write coil 6 and a wiring 7A of the erasing coil 7, a plate-like extended portion 20c connected to a flange portion 20b of the bobbin body 20a and having the width a little smaller than the width of the cut out 14, an approximately square pillar-like terminal stand 20d connected to the tip end of the extended portion 20c perpendicularly to the extended portion 20c and a plurality of metal made terminal pins 20e molded in a unit with the lower side of the terminal stand 20d and to be connected to not shown some outer terminals such as FPC. The lead 6a of the read/write coil 6 and the lead 7a of the erasing coil 7 are connected to the terminal pins 20e of the terminal stand 20d.
In the read/write coil 6, the extended portion 20c is adapted to be accommodated in the cut out 14 in the state where the approximately cylindrical bobbin body 20a is inserted in the first leg portion 10a. And, in that state the read/write coil 6 (bobbin 20) and the first leg portion 10a are bonded in a unit with the adhesive such as epoxy adhesive.
In the erasing coil 7, the extended portion 20c is adapted to be accommodated in the cut out 14 in the state where the approximately cylindrical bobbin body 20a is inserted in the third leg portion 10c. And, in that state the erasing coil 7 (bobbin 20) and the third leg portion 10c are bonded in a unit with the adhesive such as epoxy adhesive.
Further, as a similar type of magnetic head there is what is shown in FIG. 9 (hereinafter referred to as -conventional example 5"). The magnetic head 1 of the conventional example 5 comprises, as shown in FIG. 9, a first and second slider 4a and 4b which are made of non-magnetic material and form the front core 3 on one side of which a sliding surface S is formed while being formed in a unit with the front chip core 2 across the front chip core 2, the back yoke 5 to be connected to the other side of the front core 3 and the coil of the bobbin type with the terminals (the read/write coil 6 and the erasing coil 7) which is approximately the same structure as that of the conventional example 4. For reference, in FIG. 9, sign 21 is a FPC to a specific part thereof the terminal pins 20e are connected.
However, since, in the magnetic heads 1 of the conventional examples 4 and 5, the terminal stand 20d is disposed outside the back yoke 5 (outer body 8), to that extent, it is difficult to miniaturize the apparatus, and that, the leads (lead 6a, 7a) of the terminal stand 20d are easily likely to be broken during assembling or using by touching to the shutter of the disc.
In order to improve the above problems of the conventional examples 4 and 5, there are the magnetic head as shown in FIGS. 10 and 11 (hereinafter referred to as "conventional example 6").
The magnetic head 1 of this example 6 is, as shown in FIGS. 10 and 11, comparing to the conventional example 4 in FIG. 8, different mainly in that a cut outs 23 are formed at the corner portions 22 which are formed at the place where the first and second short side portions 8.sub.11 and 8.sub.12 of the back yoke 5 and the second long side portion 8.sub.22 of the back yoke 5 are joined, and that in place of the read/write coil 6 and the erasing coil 7 the structure other than the one of the type shown in FIG. 8 (the terminal stand 20d and the bobbin body 20a are separated), in which the bobbin 20 is molded in a unit, is employed.
The cut out 23 is adapted to include the neighboring portions of the corner portion 22 consisting of the bottom portion 9, of the short side portions 8.sub.11 and 8.sub.12 and the long side portion 8.sub.22.
Each bobbin 20 of the read/write coil 6 and the erasing coil 7 comprises, in general, the approximately cylindrical bobbin body 20a with which the wiring of the read/write coil 6 or the erasing coil 7 is coupled, the approximately square pillar-like terminal stand 20d held by the flange portion 20b of the bobbin body 20a, and a plurality of metal made terminal pins 20e to be connected to the outer terminals such as FPC (not shown) which are molded in a unit with the terminal stand 20d at the below side thereof. The lead 6a of the read/write coil 6 and the lead 7a of the erasing coil 7 are connected to the terminal pins 20e.
In the read/write coil 6, the terminal stand 20d is adapted to be accommodated in the cut out 23 in the state where the approximately cylindrical bobbin body 20a is inserted in the first leg portion 10a. Further, in the erasing coil 7, the terminal stand 20d is adapted to be accommodated in the cut out 23 in the state where the approximately cylindrical bobbin body 20a is inserted in the third leg portion 10c, so that the miniaturization of the magnetic head can be carried out because the terminal stand 20d is approximately accommodated in the cut out 23 or the back yoke 5.
However, in the magnetic head 1 of the conventional example 6, since the terminal stand 20d is accommodated in the back yoke, the cut out 23 of the back yoke 5 has to make large accordingly. For that reason, the shield effect becomes worse to take easily the influence of some outer noises.
Further, due to the provision of the cut out 23, the contacting area of the back yoke 5 with the front core 3 becomes small, so that, since the bonding force becomes weak, the front core 3 and the back yoke 5 are apt to peel off easily.
Further, since the front core 3 is constructed in such a manner as it bridges the cut out 23, a shock from out side to the magnetic head 1 may be damaged in the bridging portion of the front core 3 by being bent for instance.
And, since a portable note book PC (personal computer) happens to be dropped often, as to the magnetic head to be used in a thinner type of FDD for use of PC, in particular, one which has a strength against a shock is desired to be made.
The present invention has been made in the above circumstance and is to provide a magnetic head miniaturized and strong against a shock.